1. Field of the Invention
The invention relates generally to a method of optimizing the process of selective epitaxial growth. More particularly, the present invention relates to a method of optimizing the process of selective epitaxial growth, by setting a guideline for the reaction temperature, pressure, and gas ratio. A non-equilibrium factor dependent on the characteristic of the equipment and the types of source gases is then calculated using a super-saturation ratio dependent on basic thermodynamics law, since the selective epitaxial growth by CVD is a deposition method by which a product created by thermal activation of reactive gases is obtained in the shape of a thin film.
2. Description of the Related Art
In manufacturing processes of semiconductor devices, application of selective epitaxial growth technology is highly valued in view of the reduction in cell size and simplification of the process. In selective epitaxial growth by CVD, it is difficult to obtain a desired thin film shape without a comprehensive understanding of complicated technology; however, it is required that its mechanism be analyzed exactly.
As a CVD reaction is fundamentally based on a thermal chemical reaction, it depends on thermal chemical law. In particular, where a selective epitaxial growth (SEG) layer is grown by a low pressure/rapid thermal processing-chemical vapor deposition (LP/RTP-CVD) method using a Sixe2x80x94CLxe2x80x94H gas system, its applicability is increased. This is because application of the Sixe2x80x94Clxe2x80x94H gas system occurs in a high temperature process and its pressure is much higher than the selective epitaxial growth process by UHV-CVD, since it approaches to a thermodynamics reaction atmosphere in case of high temperature and pressure.
SEG by a general LP/RPT-CVD method uses a Sixe2x80x94Clxe2x80x94H gas system. So far, many experiments have been made to find out its process limits in order to grasp respective parameters related to the selective epitaxial growth, that is, dependency of temperature, pressure, and gas ratio so that the process conditions can be optimized.
Also, whenever the gas system is changed or the type of the equipment is varied, it is difficult to exactly find out the margin of the selective epitaxial growth process for the equipment. It is also difficult to find out the characteristics of the source gas.
In addition, there is no basic reference for securing selectivity for the pattern material and controlling facets and defects.
As such, since there is no guideline relating to the selective epitaxial growth process, there is a problem in that optimized points must be determined through experimentation.
The present invention provides a method of optimizing the process of selective epitaxial growth, by setting a guideline for the reaction temperature, pressure, and gas ratio and then calculating a non-equilibrium factor dependent on the characteristics of the equipment and the types of source gases, using a super-saturation ratio dependent on basic thermodynamics law, since the selective epitaxial growth by CVD is a deposition method by which a reactive product by thermal activation of a reactive gas is obtained in the shape of a thin film.
A method of optimizing the process of selective epitaxial growth according to the present invention comprises setting a guideline of the selective epitaxial growth process to the value of a super-saturation ratio for the variations in temperature, pressure, and gas ratio when the selective epitaxial growth process is performed in a LP/RPT-CVD apparatus.
Also, a non-equilibrium factor (NEF) affecting the selective epitaxial growth when the selective epitaxial growth process is performed in a LP/RPT-CVD apparatus is as follows:
NEF=[exp(lxe2x88x92(A/B))xc3x97Cxe2x88x92D]xc3x97Fxc3x97(1/S)
wherein A: actual temperature of a wafer.
B: the set temperature of the wafer.
C: relative weight relating to the type of the equipment (ranging between 1xcx9c5).
D: relative items relating to the gas mixing and the type of gas.
F: factor relating to the pressure and formation of a diffusion layer (the value increases as the pressure increases).
S: total area of the window/total area of the wafer
The present invention determines a guideline for the process, including a super-saturation curve in a situation where the temperature, pressure, and gas ratio are varied in a selective epitaxial growth process. Thus, it can optimize the growth condition by setting the range where desired epitaxial growth can occur. It also optimizes the selective epitaxial growth condition depending on respective parameters by calculating the non-equilibrium factor to determine a relative difference of the respective parameters affecting the process.